Turbochargers may improve engine torque/power output density. A turbocharger may include a compressor and a turbine connected by a drive shaft, where the turbine is coupled to an exhaust manifold side and the compressor is coupled to an intake manifold side. In this way, the exhaust-driven turbine supplies energy to the compressor to increase the pressure in the intake manifold (e.g. boost, or boost pressure) and to increase the flow of air into the engine. The boost may be controlled by adjusting the amount of gas reaching the turbine, for example with a wastegate.
Wastegates may be actuated pneumatically, hydraulically, or electrically. In one example, a wastegate may be actuated via boost pressure produced by the turbocharger. However, it may be advantageous to open the wastegate during low- or no-boost conditions, in order to reduce pumping losses and improve fuel economy. Thus, vacuum-actuated wastegates have been developed to allow for wastegate control during low boost conditions. While vacuum-actuated wastegates may provide robust wastegate control during conditions of high engine vacuum, during higher-boost conditions, the engine intake manifold vacuum used to provide vacuum to actuate the wastegate is not available. A separate vacuum pump may be provided to supply the needed vacuum when engine vacuum is not available, thus wasting fuel.
The inventors have recognized the issues with the above approach and offer a method to at least partly address them. In one embodiment, a method comprises when boost is below a threshold, generating vacuum with an actuator in a first position by flowing air from a compressor outlet to an intake manifold through a first ejector, and when boost is above the threshold, generating vacuum with the actuator in a second position by flowing air from the compressor outlet to a compressor inlet through a second ejector.
In this way, two ejectors may be provided to generate vacuum during higher boost conditions, via the second ejector positioned in the compressor flow path, and to generate vacuum during low or no boost conditions, via the first ejector positioned across the engine throttle. The flow through the ejectors may be controlled by separate motive flow control valves, in one example, which are actuated via a common actuator. In doing so, vacuum may be generated under a wide variety of operating conditions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.